凤眼莲、稻草和污泥制备生物炭的特性表征与环境影响解析

Characterization of biochar derived from water hyacinth,rice straw and sewage sludge and their environmental implications

有机废弃物限氧热解制备生物炭可在减缓温室气体排放的同时改善土壤和水体环境质量,但同时生物炭在环境中的应用具有潜在生态毒理风险.因此,在将生物炭大规模应用于各类环境介质前,对其关键物理-化学性质进行系统分析与评价是极为必要的.本文选择对我国水生生态环境危害最大的入侵植物凤眼莲(Eichhornia crassipes)和我国产量最高的农业废弃物稻草,以及市政污水处理厂剩余污泥3种生物质前体,于250~550℃进行低温慢热解,对所制备生物炭的表面形貌、元素组成、矿物形态和一系列关键化学特性进行了全面表征与比较分析.在此基础上,深入探讨了此3类生物炭应用于土壤改良、重金属污染修复和水体富营养化控制的潜力与风险.结果表明,凤眼莲生物炭中K、Ca、Na、Mg含量最为丰富,指示其对于缓解土壤酸化具有重要应用价值,而其中P主要以AlPO_4晶体态存在,水溶性较低,这有利于降低此类生物炭引起水体富营养化的风险;水稻秸秆生物炭阳离子交换量(CEC)相对较高,达到33.7 cmol·kg^(-1),表明其在提高土壤保肥能力和降低重金属生物有效性方面具有较大潜力;SEM-EDX显示,凤眼莲生物炭和稻草秸秆生物炭均具有发达的束筒结构,可优先考虑用于改善土壤通气性;但是,部分生物炭中水溶性Cd、As含量超出安全阈值,表明对有机质前体和热解产物进行严格检测和筛选是实现生物炭在环境与农业中安全利用的必要环节.

The conversion of organic residues to biochar through pyrolysis has proved to be an effective way in improving the environmental quality of soil and water while reducing the release of greenhouse gas. However, the application of biochar in the environment may simultaneously pose a range of ecotoxicological risks. Therefore, it is essential to analyze and evaluate the key chemical properties of biochars before their application in field. In this study,water hyacinth （Eichhornia crassipes）, the most aggressively invasive species, rice straw, the most prominent crop residue in China, and municipal sewage sludge have been chosen as three typical feedstocks and slowly pyrolyzed at 250, 350,450 and 550 ℃. The resultant biochars were characterized for surface morphology, element composition, mineral constituent, and a set of chemical properties pertinent to their potential use in soil improvement, remediation of heavy metal contamination and eutrophication control. According to the results, water hyacinth biochar （ WBC ） contained the highest amount of water-soluble K, Ca, Na and Mg but lowest P in water extraction, indicating its potential in mitigating soil acidification with minimized risk of eutrophication. Rice straw bioehar （RBC） exhibited the most prominent CEC （33.7 cmol.kg-1） among tested samples, which was useful to enhance minerals retention in soils while decreasing heavy metal bioavailability. As shown by SEM-EDX, bundled tube structure was developed in W-BC and R- BC, which could be used with priority to improve soil aeration. However, water-soluble Cd and As in some biochar samples exceeded the safety threshold, highlighting the necessity of pre-screening of both feedstocks and biochar products for their safe application in environment and agriculture.